Global Navigation Satellite Systems (GNSS) is a collective term covering various types of satellite navigation technologies, such as the Global Positioning System (GPS). Assisted-GNSS (A-GNSS) enables faster position determination in a mobile wireless device than can be obtained using only the broadcast GNSS satellite data, by providing assistance data from the wireless network, such as ephemeris data, clock corrections, and reference locations. The A-GNSS technology has been standardized in the Open Mobile Alliance (OMA) standard: Open Mobile Alliance, User Plane Location Protocol Candidate Version SUPL2.0: OMA-TS-ULP-V2—0-20091208-C, December 2009.
Open Mobile Alliance (OMA) SUPL (Secure User Plane Location protocol) Release 1 (SUPL1.0), Release 2 (SUPL2.0), and Release 3 (SUPL3.0) have considerable differences in their A-GNSS capabilities due to technical evolution and improvements added in the later releases. Also, a carrier's proprietary A-GNSS services and features may offer better performance than the standardized solutions.
The Third Generation Partnership Project (3GPP) defines A-GNSS positioning protocols for GERAN (GSM EDGE Radio Access Network), UTRAN (UMTS Terrestrial RAN) and E-UTRAN (Enhanced UTRAN) or LTE (Long-Term Evolution). The positioning protocols for CDMA (Code Division Multiple Access) networks are defined by 3GPP2. The assistance may include the navigation model (orbit and clock parameters), reference location and reference time. In an assisted situation, the receiver does not need to download the navigation model from the satellites, but receives it over the cellular network to significantly reduce the time to first fix and enable accurate positioning in adverse signal conditions. Each 3GPP location protocol includes carrier-specific items such as time difference and round trip time measurements and different formats for orbit and clock parameters, reference location and reference time. Carriers are at liberty to charge different rates for these services.